With recognition of conventional non-degradable plastics, such as nylon, polyethylene terephthalate, polypropylene, and polyethylene, as a primary cause of environmental pollutions, biodegradable polyesters have been on the spotlight for environmental protection purposes. Biodegradable polyesters may be prepared by a batch production method or a continuous production method.
In the batch production method, a relatively long time that a reaction mixture spends in a reactor at a high temperature is needed to achieve an intrinsic viscosity and a molecular weight of a target polyester; a partially heterogeneous reaction may occur even in the reactor; and physical properties of the polyester may be changed at the initial, intermediate, and latter stages of a discharge process even after the completion of the reaction. In this regard, when a biodegradable polyester spends at a high temperature for a long period of time, the biodegradable polyester may be hydrolyzed by heat, which may affect mechanical strength and hydrolysis-resistant properties of the biodegradable polyester and may cause a difference in quality due to the partially heterogeneous reactions and different discharge times.
Meanwhile, the continuous production method may suppress the hydrolysis of biodegradable polyesters caused by heat generated in the batch production method. The continuous production method is appropriate for mass production and to continuously obtain products with a uniform quality.
In general, diols such as 1,4-butanediol may be used as aliphatic dihydroxy compounds to prepare biodegradable polyesters. However, 1,4-butanediol may be changed into tetrahydrofuran during a reaction, frequently causing troubles in a vacuum line of a manufacturing system. Furthermore, such 1,4-butanediol is required in excess amount. Therefore, there are needs for improvements in this regard.